The invention relates to an apparatus for trueing cylindrical articles and, more particularly, it relates to rolls of skewed-roll machines for trueing cylindrical metal articles.
The disclosed trueing rolls can be employed in skewed-roll trueing machines for trueing the entire length of cylindrical metal articles, either solid or hollow, wherein the diameter of the end portions of the articles exceeds the diameter of the central portion, e.g. tubes and pipes with flaring ends, shafts with thickened end portions, etc.
Known in the art are skewed roll couples for trueing tubes and rods of a circular cross-section. These couples are usually provided with at least one skewed couple of bending rolls, offset with respect to the trueing axis and mounted intermediate support roll couples, at least one couple performing the trueing of the article by bending. The opposing rolls in such couples are spaced so and mounted at such an angle with respect to each other that upon the rotation of the rolls the article being trued should be subjected to the required pulling effort. During the trueing operation, the trued portion of the article is supported by two supporting side coupled rolls and is bent by the central bending roll couple, offset from the trueing axis. With the article rotating, it is subjected to sign-variable elasto-plastic bending or flexing required for eliminating the curvature of the trued portion of the article. Owing to the trueing rolls being mounted at an angle to the trueing axis, the article is driven through a helical motion and, with the article rotating, it is subjected to repeated sign-variable elasto-plastic bending or flexing and trueing throughout the entire length thereof, in every plane including the longitudinal axis of the article. To handle a broad range of sizes of tubes and rods, the present-day skewed-roll trueing machines incorporate mechanisms for adjusting the spacing of the trueing rolls and the angle of their inclination with respect to the trueing axis.
There are also known single skewed rolls mounted in trueing machines in a checkered order, i.e., the rolls of one row being support or back-up ones and the rolls of an adjacent row being bending ones ensuring that an article is bent while being trued, owing to their axes being offset from the trueing axis. These rolls are used for trueing by flexing both cylindrical articles having no thickened ends and the narrow central portions of cylindrical articles having thickened ends. In this case the trueing of the articles with thickened ends does not require the resilient suspension of the single rolls, since the thickened end of the article throughout the trueing operation rides free of the single rolls and passes unobstructedly between the rows of the rolls, while the narrow central portion is being trued by sign-variable bending or flexing. However, with this roll arrangement the thickened ends are not trued and just pass free through a trueing machine.
With the usual fixed arrangement of roll couples the spacing of the opposing rolls does not vary during a trueing operation. Whereby it is virtually impossible to true articles with thickened ends, because in the process of a trueing operation it is impractical to increase the spacing of the opposing rolls of the couples to let pass the thickened end of an article. To true articles with thickened ends, resilient suspension of the rolls has been resorted to, with the rolls being mounted by means of shock absorbers. In resiliently mounted roll couples the narrow central portion of an article with thickened ends can be trued, because during the trueing operation the roll couples are able to spread with aid of their resilient mountings to let the thickened end of an article pass, whereafter they move back closer together to true the narrow portion of an article. However, this trueing has proved to be of inadequate accuracy, since only the narrow portion of the article is really trued, whereas the thickened ends thereof remain untrued.
There are further known rolls for trueing articles with end portions of an increased diameter, such as tubes with outwardly offset or flaring ends, mounted in three-roll sets associated with mechanisms for pre-spacing of the sidemost rolls of these three-roll sets prior to trueing an article, e.g. a tube, so as to ensure that the spacing of the rolls provides for the passage of the outwardly offset end of the article, i.e. of the tube. The arrangement of such rolls includes two three-roll support or back-up sets, there being mounted centrally intermediate these two three-roll support sets a single bending role offset with respect to the trueing axis, designed to bend an article, e.g. a tube to be trued. In the process of the trueing operation the article, e.g. a tube is driven through a helical motion, each portion, bearing upon the three-roll support or back-up sets, being bent by the bending roll and trued by sign-variable bending or flexing. However, these rolls, the same as the previously described ones, are capable of trueing only the narrow portions of an article, e.g. a tube, while the thickened, e.g. flaring or outwardly offset ends of the article pass through without trueing.
Thus, all the hitherto known sets of skewed rolls of trueing machines do not provide for trueing the thickened end portions of an article, their sole function being that of trueing the narrow portion of the article, the thickened end portions thereof are let through without trueing. This may be explained by the fact that all the hitherto known rolls used for trueing articles of a cylindrical shape with thickened end portions would not provide for trueing the thickened ends of the articles in a roll set made up by two rolls.
There are widely known rolls for trueing cylindrical articles in a single two-roll set consisting of a single support or back-up roll and a single pressure or bending roll, both rolls being mounted at an angle to the trueing axis. In such a roll set the support roll is concave, and the pressure roll either convex or cylindrical. While being trued, the portion of the article, which is being acted upon, bears upon the two side contact areas of the support roll and is bent by the central contact area of the bending pressure roll.
However, the profiles of this known single roll couple do not provide for trueing the thickened end portions of cylindrical articles.
The unavailability of rolls capable of trueing the thickened end portions of cylindrical articles requires the use of auxiliary equipment for the purpose, which affects the overall productivity of labor and increases the cost of trueing.